This invention is concerned with monitoring electronic systems.
In particular, but not exclusively, the present invention is concerned with equipment for facilitating the diagnostic testing/monitoring of mobile telephone units or more generally mobile transmitter/receiver units.
A particular form of such mobile communication system is known as a cellular mobile communications system.
For convenience and without limitation of the scope of the practical application of the methods and apparatus of the invention, for the purposes of facilitating discussion of such methods and apparatus of the invention, the use thereof in relation to a cellular mobile communication system will be considered in detail.
In brief, a cellular mobile communication system is a communication network involving a number of so-called cells which makes it possible for a transmitter/receiver unit installed in a motor or other vehicle, to communicate with conventionally provided telecommunications systems by way of a network of transmitter/receiver aerials or beacons each defining the `focal point` or node of a cell and each of which are so positioned in predetermined locations relative to each other across the zone or region within which the network is designed to be operative, as effectively to form inter-related groups of cells.
In a known system, each cell group includes seven individual cells whose arrangement within a group can be likened to a honeycomb. In this system the groups themselves are mutually arranged within the system so as to expand the extent of operation of the group honeycomb.
Each cell includes a beacon which is responsive to a predetermined number of channels selected from the total number of channels (amounting to several hundred) involved in the overall system. In addition, each such cell of a group has uniquely ascribed thereto a particular group of the channels whereby no two adjacent cells in the overall system have precisely the same channel grouping.
The underlying concept is that when a mobile transmitter/receiver unit is located within the effective area of any one beacon and the user thereof requires to communicate with a particular telephone number, national or otherwise, the mobile equipment enables him to dial, in a manner similar to the dialling of a conventional telephone the required number. The mobile equipment is capable of opening a communication channel to the required telephone subscriber by way of the beacon in the cell within which the vehicle happens to be located at the time of initiating operation of the equipment.
As the vehicle with the mobile unit moves further away from any one beacon and moves nearer to any other beacon in the system, the system itself, where necessary, automatically transfers the communication path from beacon to beacon.
Control arrangements provided within the beacon network of the system, and those involved in the mobile equipment ensures that any communication link that has been established is maintained as the vehicle moves from the ambit of one beacon to that of the next beacon along the route of the vehicle. Thus the mobile unit is automatically effectively transferred from one beacon to another without any interference with (i.e., breaking the communication connection established) the communication path between the mobile unit and the called number. These operations are effected without any action by the user.
From the forgoing it will be appreciated that the equipment involved is highly complex, and that having regard to this complexity it has been found that it is essential that the actual mobile units involved should always operate within their operational specifications to ensure the optimum operational efficiency of the system overall.
It will also be appreciated that since the communication system involves provision of a very large number of relatively narrow (frequency-wise) communication channels between the mobile telephone units and the network of so-called base channels it is important that any mobile telephone unit should always operate within the frequency limits of any channel to which it is allocated so as to avoid any operational interference between channels.
In practice, if the operational parameters of any mobile telephone unit should drift in such manner that the operational bandwidth thereof overlaps the frequency limits of adjacent channels any mobile telephone unit allotted to these adjacent channels may well be prevented from efficient operation.
A further problem arises in that the operation of a telephone unit whose operational frequency has spread i.e., whose frequency response has drifted, outside the allowed band width of a channel, can adversely affect the transfer of telephone communication paths from node to node.
With regard to this known equipment, experience has shown that it is not until the user of the telephone notices, normally during actual use of the equipment, that the performance of the mobile telephone is not as good as expected or as previously experienced does the user consider taking corrective action to have the mobile telephone equipment involved tested and, if necessary, repaired.
It will be apparent that by the time the actual user has realized that the equipment has become defective there is every possibility that progressive ongoing malfunctioning equipment could have reached the stage in which it is and may have been for a considerable period of time seriously adversely interacting with the equipment of other users, and thereby reducing the efficiency of operation of such other user's equipment and also the operation of the system overall.